Scientific name: Nuttallia obscurata

What Is It?

Nuttallia obscurata, commonly known as the purple varnish, or mahogany clam was first introduced to the United States and Washington from ship ballast water from Asia It is freshwater tolerant and is most abundant in areas where there is freshwater runoff.

Is It Here Yet?

Yes. The purple varnish clam has been reported in northern Puget Sound for about 10 years. Dense colonies can be found on the San Juan Islands in densities exceeding 800 per square meter.

Why Should I Care?

The purple varnish clam grows prolifically, forming dense colonies very rapidly and displacing native species. It can be harmful to humans because of its higher level of toxins.

How Can We Stop It?

To prevent spread, clean, drain, and dry your equipment after each use.

What Are Its Characteristics?

  • Corbula amurensis is a tan, white, or yellow clam, up to about 25 mm long.
  • The ‘overbite’ clam, derives its name from the right half of the shell being larger than the left and slightly overbiting its lower margin.
  • The shell has the overall shape of a broad isosceles triangle.
  • In younger clams the shell surface is covered by a thin, smooth tissue, but in older clams the tissue becomes wrinkled around the lower margin.
  • Corbula amurensis is primarily subtidal, but is occasionally abundant on intertidal mudflats.

Additional Photographs